# Plus42 — Enhanced HP-42S Calc Simulator > Advanced scientific programmable RPN calculator simulator with enhanced features. (iPhone/iPad app by Thomas Okken.) - Source: https://appshunter.io/ios/app/plus42/id1597963622 (this page in markdown: same URL + `.md`) - Developer: [Thomas Okken](https://appshunter.io/developer/337692632) - Category: Utilities - Price: $9.99 - Rating: 4.90/5 from 79 App Store ratings · 39 written reviews indexed - Age rating: 4+ - Requires: iOS 12.0 · 11 MB - Languages: American English - Released: 2022-04-28 - Data updated: 2026-09-10 - Monetization: free - User reviews in markdown: https://appshunter.io/ios/app/plus42/id1597963622/reviews.md ## What is Plus42? Plus42 is an advanced scientific programmable calculator, based on Free42. Free42, in turn, is a complete re-implementation of the HP-42S scientific programmable RPN calculator, which was made from 1988 until 1995 by Hewlett-Packard. Free42 is a complete rewrite and contains no HP code whatsoever. Plus42 builds on Free42 and adds: Algebraic expressions modeled after those used on the HP-27S and HP-17B/19B; attached units and unit conversions modeled after those used on the HP-48/49/50 series; directories for more organized storage of programs and variables; a larger display, with 8 rows and 22 columns (131x64 pixels) by default, which the user may resize at will; time value of money and amortization schedules; and two-dimensional plotting of functions, with ability to zoom and pan, and find integrals and roots from points in the plot. ## Key features - HP-42S RPN calculator simulation - Algebraic expressions - Attached units and conversions - Program and variable directories - Resizable 8-row, 22-column display - Time value of money and amortization - 2D function plotting with zoom and pan ## Chart rankings - #147 in Top Paid · Utilities (US App Store) ## Recent user reviews (10 of 39) All indexed reviews: https://appshunter.io/ios/app/plus42/id1597963622/reviews.md ### 5/5 — Plus42 fanatic simulator *2026-07-19, version 1.3.15* This is a fantastic HP-42S simulator. Very functional, I use it daily. My HP calculator has long been dead and this allows me to use an RPN scientific calculator in daily engineering tasks. Thank you. ### 1/5 — Not worth of it *2026-05-09, version 1.3.15* Don’t waste your money! ### 5/5 — Best calculator app! *2026-01-15, version 1.3.13* I *LOVE* Free42 Plus42 is even better! ### 5/5 — Perfection *2026-01-12, version 1.3.12* Once you use an RPN calculator, you will never go back. The HP-42S beats the HP Prime in layout and ease of use for most task, and the enhancements in this implementation is great. I love having the (enhanced) HP-42S always with me on my iPhone whenever I need a calculator. ### 2/5 — Can’t convert from DMS to decimal degrees! *2026-01-09, version 1.3.12* WTF. It can easily convert decimal degrees to DMS, but not DMS to decimal degrees?!? What is the point of having one but not the other?!? ### 5/5 — Great calculator, however *2025-12-24, version 1.3.12* I’ve really like this calculator however lately there seems to be an issue with programming. I had a program for the sulfur to convert Celsius to Fahrenheit and vice versa but for some reason it doesn’t work anymore so 212 Fahrenheit should be 100 Celsius. it comes up with something like minus one point something to the power of 6000 I wonder what the issue is? ### 5/5 — The Perfect Calculator *2025-10-28, version 1.3.11* The 42s was, in my opinion, the most elegant calculator ever devised during the golden age of HP engineering. This simulator perfectly recreates this legendary calculator and it adds some additional great features. It has several enhancements seen in the RPL calculators without introducing the shortcomings of the more complex interface. Put another way, this calculator is what HP should have done with the 48 line. I believe that Plus42 now deserves the crown of the best calculator. It is the perfect continuation of the RPN days, and since it lives on your phone, it is always at hand. All that for just under $10! ### 5/5 — Wow *2025-10-01, version 1.3.10* Can’t believe how happy this app makes me, to once again have my favorite calculator in hand. The HP-42S was unmatched and this app replicates it perfectly. Simply amazing. Thank you! ### 5/5 — Super Implementierung *2025-06-08* Ich nutze den Rechner jetzt schon seit längerem (in der Plus-Version). Bin sehr begeistert, echt super!!! Auch das Programmieren funktioniert „wie gewohnt“ (wie früher), echt cool, danke! ### 5/5 — What a delight! *2025-02-28, version 1.2.6* I can’t believe I missed Thomas Okken’s free42 and plus42 projects until now, over 20 years after his first release it appears. It’s been a joy to get reacquainted with RPN and now have the same calculator on my phone, which I have on me all the time, as I have at my desk in physical form via SwissMicros’ DM42n that just arrived. Having a physical calculator at my fingertips that I love to use is something I haven’t experienced in probably 30 years, since college. The astro navigation and conversion apps I pulled down and loaded from Thomas’ website this morning is what prompted me to write this review. Thank you Thomas for this gift to us all! You’ve left no detail out for someone like me. ## Frequently asked questions about Plus42 ### What is Plus42? Plus42 is an advanced scientific programmable calculator that simulates the functionality of the classic HP-42S RPN calculator. It builds upon the Free42 project, offering enhanced features like algebraic expressions, unit conversions, and 2D plotting. ### What are the key features of Plus42? Key features include an HP-42S RPN simulation, algebraic expressions similar to HP-27S, attached units and conversions, directories for organizing programs and variables, a resizable large display, financial functions like TVM and amortization, and 2D plotting with zoom, pan, and root/integral finding. ### Is Plus42 free to use? Yes, Plus42 is a free application. The provided information indicates it does not have in-app purchases or advertisements, suggesting a completely free experience for users. ### What kind of calculator is it based on? It is based on the HP-42S scientific programmable RPN calculator, which was manufactured by Hewlett-Packard from 1988 to 1995. Plus42 is a re-implementation and enhancement of the Free42 project, which itself is a rewrite of the HP-42S. ### Who would benefit from using Plus42? This app is ideal for students, engineers, scientists, and anyone who requires a sophisticated scientific calculator with RPN input. Users who appreciate the legacy of Hewlett-Packard calculators or need advanced features like unit conversions and plotting will find it particularly useful. ## Version history (last 5 releases) ### 1.3.15 — 2026-05-05 Fixed RLN and RRN for negative numbers in BSIGNED mode. ### 1.3.14 — 2026-04-22 Fixed crash in REFMOVE. More accurate GAMMA for integer arguments. ### 1.3.13 — 2026-01-14 Fixed potential crash in VARMENU. ### 1.3.12 — 2025-10-29 Fixed crash in menu logic. ### 1.3.11 — 2025-10-16 Fixed crash in EQN->R/S when EQNS does not yet exist. When a new program was created by inserting END, the new program could end up being locked initially. Fixed. ## Apps similar to Plus42 | App | Rating | Price | Category | | --- | --- | --- | --- | | [HP-35](https://appshunter.io/ios/app/hp-35/id6738010641) | 5.0 (5) | Free | Utilities | | [RPN-25 CE](https://appshunter.io/ios/app/rpn-25-ce/id1529311398) | 4.6 (9) | $2.99 | Utilities | | [RLM-11CX](https://appshunter.io/ios/app/rlm-11cx/id1630739014) | 3.1 (7) | Free | Utilities | | [TechniCalc Calculator](https://appshunter.io/ios/app/technicalc-calculator/id1504965415) | 4.7 (81) | $7.99 | Utilities | | [RPN-67 SD](https://appshunter.io/ios/app/rpn-67-sd/id1109722386) | 4.6 (17) | $3.99 | Utilities | | [HP 15c Calculator](https://appshunter.io/ios/app/hp-15c-calculator/id503720774) | 4.8 (207) | $14.99 | Utilities | ## More apps by Thomas Okken - [Free42](https://appshunter.io/ios/app/free42/id337692629) - [Life II](https://appshunter.io/ios/app/life-ii/id1621692220) All apps by Thomas Okken: https://appshunter.io/developer/337692632 --- *Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-09-10.*